Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$49.70	5.597%	$52.4817	$52.48	$52.50	$52.50
Purchase #2	$139.29	9.158%	$152.0462	$152.05	$152.05	$152.00
Purchase #3	$129.61	5.565%	$136.8228	$136.82	$136.80	$136.80
Purchase #4	$230.26	6.726%	$245.7473	$245.75	$245.75	$245.70
Purchase #5	$99.25	12.521%	$111.6771	$111.68	$111.70	$111.70
Purchase #6	$157.90	12.674%	$177.9122	$177.91	$177.90	$177.90
Purchase #7	$196.81	13.218%	$222.8243	$222.82	$222.80	$222.80
7 purchase totals =	$1,002.82		$1,099.5116	$1,099.51	$1,099.50	$1,099.40